Intrahepatic MxA and PKR protein expression in chronic hepatitis C virus infection

Recent updates of interferon-derived myxovirus resistance protein A as a biomarker for acute viral infection

BACKGROUND

Antibiotic resistance (AMR) remains a global public health threat with a high burden in sub-Saharan countries. The overuse of antimicrobials in the clinical setting is the main factor for the spread of antibiotic resistance. Diagnostic uncertainty in differentiating between bacterial and viral infections is the major contributor to antimicrobial overuse. The available biomarkers lack specificity in guiding clinicians to make antibiotic decisions and only estimate bacterial infection.

MAIN BODY

Myxovirus resistance (Mx) proteins are a type of interferon (IFN)-inducible protein that belongs to the dynamin superfamily of large guanine triphosphates (GTPases) involved in broad antiviral responses. Myxovirus resistance protein A (MxA) is a host-derived biomarker with antiviral properties against various viruses. It is induced by IFN I and IFN III as part of the innate immune response. Its basal level is < 15 ng/ml and elevated levels are detectable 1-2 h after IFN induction and remain detectable in serum up to 10 days after viral infection. Increased levels in the blood are associated with viral infection and remain low during bacterial infections. This biomarker showed promising performance in diagnosing undifferentiated febrile patients with respiratory tract infections. In this review, we discuss the role of Mx proteins, specifically MxA, in diagnosing acute viral infections, including how they are induced and their potential as diagnostic tools.

METHODS

A comprehensive electronic search was conducted in Scopus and Medline (using the PubMed interface) regarding myxovirus resistance protein A as a biomarker for acute viral infection. In the search strategy, English language was used without date restriction. Manual search was also performed when appropriate.

CONCLUSIONS

Elevated MxA combined with other biomarkers, such as CRP and PCT, is a promising tool for identifying patients with viral infections. Therefore, incorporating MxA in the existing point of care formats help to improve the antibiotic stewardship programs and future randomized controlled trials are recommended to evaluate its utility in medical practice.

MxA is a positive regulator of type I IFN signaling in HCV infection

Type I interferons (IFNs) are a family of primordial cytokines that respond to various pathogen infections including Hepatitis C virus (HCV). Type I IFNs signal through Jak/STAT pathway leading to the production of a few hundred interferon stimulated genes (ISGs). The aim of this study was to explore the role of one of these ISGs, MxA in HCV infection and type I IFN production. Plasmid encoding MxA was cloned into PcDNA3.1-3×tag vector and MxA expression was confirmed both at mRNA (RT-PCR) and protein (Western blot, WB) levels. IFNα and IFNβ productions were quantified by RT-PCR from cell lysate and by ELISA kit from culture medium following MxA over-expression in Huh7.5.1 cells. The activation status of Jak/STAT signaling pathway was examined at three levels: p-STAT1 (WB), interferon sensitive response element (ISRE) activity (dual luciferase reporter gene assay), and levels of ISG expression (RT-qPCR). J6/JFH1 HCV culture system was used to study the role of MxA in HCV replication. Our findings indicated that MxA over-expression inhibited HCV replication and potentiated the IFNα-mediated anti-HCV activity; MxA stimulated the production of IFNα, IFNβ, and enhanced IFNα-induced activation of Jak-STAT signaling pathway. We concluded that MxA is a positive regulator of type I IFN signaling in HCV infection.

Immunohistochemical Evaluation of Mx Protein Expression in Canine Encephalitides

Mx proteins are a group of interferon-induced GTPases whose expression has been demonstrated in a number of human viral infections and in some idiopathic inflammatory diseases. In this study, the expression of Mx protein was evaluated in known viral, nonviral, and idiopathic encephalitides in the dog via immunohistochemistry using an antibody against human MxA. All 12 cases of confirmed viral encephalitis, including 7 cases of canine distemper, 4 cases of canine herpesvirus, and 1 case of rabies, were Mx positive. In canine distemper cases, staining was particularly strong and a variety of cell types were positive, including astrocytes, macrophages/microglia, and neurons. Immunoreactivity for Mx protein was evident in a few cases of nonviral infectious encephalitis, including neosporosis (1/1), Chagas disease (2/3), aspergillosis (1/2), and encephalitozoonosis (1/1). Consistent staining was observed in most cases of idiopathic encephalitis, including granulomatous meningoencephalomyelitis (7/7), necrotizing meningoencephalitis of pug dogs (6/7), and necrotizing encephalitis of the Yorkshire Terrier (3/3) and Maltese (1/1) breeds. Mx staining was negative in 5 normal dog brains; 3 cases of cryptococcosis; and single cases of blastomycosis, protothecosis, and bacterial meningitis.

HCV Infection and Interferon-Based Treatment Induce p53 Gene Transcription in Chronic Hepatitis C Patients

It is suggested that the tumor suppressor p53 gene, classified as an interferon-stimulated gene, is implicated in the interferon (IFN)-mediated innate immunity against viruses. This study aimed to examine the transcriptional response of the p53 gene to hepatitis C virus (HCV) infection and IFN-based therapy in chronic hepatitis C (CHC) patients. The study included 65 CHC patients (HCV genotype 1), treated with pegylated IFN-α and ribavirin, and 51 healthy individuals. p53 gene expression was quantified by real-time polymerase chain reaction in peripheral blood mononuclear cells (PBMCs). Analyses were performed before and at weeks 4 and 12 of treatment. p53 gene expression was significantly upregulated in CHC patients compared with healthy controls and at week 4 of therapy. No significant differences in p53 mRNA expression between rapid virologic responders, complete early virologic responders, and nonresponders were observed. No significant correlation was found between p53 gene expression and viral load. The results obtained indicate that HCV infection and IFN-based treatment induces p53 gene transcription in PBMCs. The p53 gene may therefore play a role in HCV infection but is not directly involved in treatment-induced HCV elimination. Moreover, variations in p53 gene expression do not determine on-treatment response in patients with chronic HCV genotype 1 infection.

IFN-λ: A New Class of Interferon with Distinct Functions-Implications for Hepatitis C Virus Research

Pegylated interferon-α and ribavirin (PEG-IFN/RBV) is widely used to treat chronic hepatitis C virus infection with notorious adverse reactions since the broad expression of IFN-α receptors on all nucleated cells. Accordingly, a Type III IFN with restricted receptors distribution is much safer as an alternative for HCV therapy. In addition, single nucleotide polymorphisms (SNPs) near the human IFN-λ3 gene, IL-28B, correlate strongly with the ability to achieve a sustained virological response (SVR) to therapy with pegylated IFN-α plus ribavirin in patients infected with chronic hepatitis C. Furthermore, we also discuss the most recent findings: IFN-λ4 predicts treatment outcomes of HCV infection. In consideration of the apparent limitations of current HCV therapy, especially high failure rate and universal side effects, prediction of treatment outcomes prior to the initiation of treatment and developing new alternative drugs are two important goals in HCV research.

Cell-type specific interferon stimulated gene staining in liver underlies response to interferon therapy in chronic HBV infected patients

BACKGROUND

Interferon-α is approved as one of the main therapeutic treatments for chronic hepatitis B virus infection, but only a small number of patients achieve sustained virological response. The molecular mechanisms underlying IFN-α resistance in those patients who do not respond remain elusive. Previous work in our laboratory identified the pre-activation of IFN signaling leading to increased expression of a subset of interferon stimulated genes in the pretreatment liver tissues of chronic HBV infected patients correlated with treatment non-response.

AIMS

We studied the cell-type specific gene expression of interferon stimulated genes in the liver of chronic HBV infected patients and the cellular basis of the phenotype through ISG15 and MxA protein expression.

METHODS

Immunohistochemical analysis was used to detect the expression of ISG15 and MxA protein in the pretreatment liver tissues of chronic HBV infected patients and the expression patterns were correlated with treatment outcomes.

RESULTS

In the non-responders, ISG15 and MxA protein expression in the pretreatment liver tissues was more pronounced in hepatocytes while in the responders, ISG15 and MxA protein expression was more focused in macrophages. ISG15 and MxA proteins were occasionally expressed in hepatocytes in normal livers.

CONCLUSION

There were significant differences in the cell-type specific protein expression of ISG15 and MxA in the pretreatment liver tissues of chronic HBV infected patients between treatment responders and non-responders. An easy prediction method based on immunohistochemical stains of a subset of interferon stimulated genes may be developed to predict treatment outcomes of IFN therapy in chronic HBV infected patients.

Implication of protein kinase R gene quantification in hepatitis C virus genotype 4 induced hepatocarcinogenesis

BACKGROUND

Protein kinase RNA (PKR-regulated) is a double-stranded RNA activated protein kinase whose expression is induced by interferon. The role of PKR in cell growth regulation is controversial, with some studies supporting a tumour suppressor function and others suggesting a growth-promoting role. However, it is possible that the function of PKR varies with the type of cancer in question.

METHODS

We report here a detailed study to evaluate the function of PKR in hepatitis C virus genotype 4 (HCV-4) infected patients. PKR gene was quantitated in HCV related malignant and non-malignant liver tissue by RT-PCR technique and the association of HCV core and PKR was assessed.

RESULTS

If PKR functions as a tumour suppressor in this system, its expression would be higher in chronic hepatitis tissues. On the contrary our study demonstrated the specific association of HCV-4 with PKR expressed in hepatocellular carcinoma (HCC) tissues, leading to an increased gene expression of the kinase in comparison to chronic hepatitis tissues. This calls into question its role as a tumour suppressor and suggests a positive regulatory role of PKR in growth control of liver cancer cells. One limitation of most of other studies is that they measure the levels rather than the quantitation of PKR gene.

CONCLUSION

The findings suggest that PKR exerts a positive role in cell growth control of HCV-4 related HCC, obtaining a cut-off value for PKR expression in liver tissue provides the first evidence for existence of a viral activator of PKR.

VIRTUAL SLIDES

The virtual slide(s) for this article can be found here: http://www.diagnosticpathology.diagnomx.eu/vs/1267826959682402.

Interferon-stimulated gene pathways in the treatment of viral hepatitis

Viral hepatitis has been treated empirically for more than 30 years with interferon (IFN)-based therapies, although in the early days of the IFN era, very little was known regarding the mechanisms of action through which IFN acts and the strategies that viruses deploy to escape the antiviral state induced by the activation of the IFN system. Over the years, we have learned how key effector molecules in this system are expressed and interact. On the verge of novel, IFN-free regimens for viral hepatitis, we can take advantage of this huge bulk of research data in order to gain better understanding of how resistance to IFN develops in our patients, to use IFN more effectively in conjunction with other drugs and to devise new treatments.

Liver protein profiling in chronic hepatitis C: identification of potential predictive markers for interferon therapy outcome

The current anti-hepatitis C virus (HCV) therapy, based on pegylated-interferon alpha and ribavirin, has limited success rate and is accompanied by several side effects. The aim of this study was to identify protein profiles in pretreatment liver biopsies of HCV patients correlating with the outcome of antiviral therapy. Cytosolic or membrane/organelle-enriched protein extracts from liver biopsies of eight HCV patients were analyzed by two-dimensional fluorescence difference gel electrophoresis and mass spectrometry. Overall, this analysis identified 21 proteins whose expression levels correlate with therapy response. These factors are involved in interferon-mediated antiviral activity, stress response, and energy metabolism. Moreover, we found that post-translational modifications of dihydroxyacetone kinase were also associated with therapy outcome. Differential expression of the five best performing markers (STAT1, Mx1, DD4, DAK, and PD-ECGF) was confirmed by immunoblotting assays in an independent group of HCV patients. Finally, we showed that a prediction model based on the expression levels of these markers classifies responder and nonresponder patients with an accuracy of 85.7%. These results provide evidence that the analysis of pretreatment liver protein profiles is valuable for discriminating between responder and nonresponder HCV patients, and may contribute to reduce the number of nonresponder patients exposed to therapy-associated risks.

Ribavirin enhances IFN-α signalling and MxA expression: a novel immune modulation mechanism during treatment of HCV

The nucleoside analogue Ribavirin significantly increases patient response to IFN-α treatment of HCV, by directly inhibiting viral replication. Recent studies indicate that Ribavirin also regulates immunity and we propose that Ribavirin enhances specific interferon sensitive gene (ISG) expression by amplifying the IFN-α-JAK/STAT pathway. We found that IFN-α-induced STAT1 and STAT3 phosphorylation was increased in hepatocytes co-treated with Ribavirin and IFN-α, compared to IFN-α alone. Ribavirin specifically enhanced IFN-α induced mRNA and protein of the anti-viral mediator MxA, which co-localised with HCV core protein. These novel findings indicate for the first time that Ribavirin, in addition to its viral incorporation, also enhances IFN-α-JAK/STAT signalling, leading to a novel MxA-mediated immuno-modulatory mechanism that may enhance IFN-α anti-viral activity against HCV.

Differential expression of interferon-induced microRNAs in patients with chronic hepatitis C virus infection treated with pegylated interferon alpha

There have been reports of in-vitro interferon (IFN)-mediated antiviral activity against the hepatitis C virus (HCV) through microRNAs (miRNAs). The main aim of this study was to evaluate the expression of several miRNAs (miR-1, miR-30, miR-128, miR-196, miR-296) in peripheral blood mononuclear cells (PBMCs) from healthy individuals after in vitro IFN-treatment and in PBMCs from patients with chronic hepatitis C (CHC) before and 12 hours after the first injection of pegylated IFN alpha. We demonstrated that expression of these miRNAs could be recorded in PBMCs collected from healthy individuals before and after in-vitro IFN alpha treatment. Our analysis revealed that the levels of expression of all miRNAs investigated in patients with CHC were different to those in healthy individuals. When levels of the miRNAs were measured 12 hours after the first IFN injection, increases in expression levels of IFN-induced miRNAs were observed in 25-50% of patients, depending on the type of miRNA examined. No correlations were observed between HCV viral load, alanine aminotransferase status and expression of miRNA. Together these findings suggest that: (i) IFN alpha in-vitro treatment of PBMCs leads to a transcriptional induction of all miRNAs investigated; (ii) miRNAs can be induced differentially by IFN treatment in patients with HCV. Given the importance of miRNAs in defending the host against virus infections, it is possible that IFN-induced miRNAs may represent an important determinant of the clinical outcome of IFN therapy in HCV infection.

Hepatitis C virus infection impairs IRF-7 translocation and Alpha interferon synthesis in immortalized human hepatocytes

Hepatitis C virus (HCV) establishes chronic infection in a significant number of infected humans, although the mechanisms for chronicity remain largely unknown. We have previously shown that HCV infection in immortalized human hepatocytes (IHH) induces beta interferon (IFN-β) expression (T. Kanda, R. Steele, R. Ray, and R. B. Ray, J. Virol. 81:12375-12381, 2007). However, the regulation of the downstream signaling pathway for IFN-α production by HCV is not clearly understood. In this study, the regulation of the IFN signaling pathway following HCV genotype 1a (clone H77) or genotype 2a (clone JFH1) infection of IHH was examined. HCV infection upregulated expression of total STAT1 but failed to induce phosphorylation and efficient nuclear translocation. Subsequent study revealed that HCV infection induces IFN-stimulated response element activation, as evidenced by upregulation of 2',5'-oligoadenylate synthetase 1. However, nuclear translocation of IRF-7 was impaired following HCV infection. In HCV-infected IHH, IFN-α expression initially increased (up to 24 h) and then decreased at later time points, and IFN-α-inducible protein 27 was not induced. Interestingly, HCV infection blocked IRF-7 nuclear translocation upon poly(I-C) or IFN-α treatment of IHH. Together, our data suggest that HCV infection enhances STAT1 expression but impairs nuclear translocation of IRF-7 and its downstream molecules. These impairments in the IFN-α signaling pathway may, in part, be responsible for establishment of chronic HCV infection.

Cell-type specific gene expression signature in liver underlies response to interferon therapy in chronic hepatitis C infection

BACKGROUND & AIMS

Chronic hepatitis C virus (CHC) infection is treated with interferon/ribavirin, but only a subset of patients respond. Treatment nonresponders have marked pretreatment up-regulation of a subset of interferon stimulated genes (ISGs) in their livers, including ISG15. We here study how the nonresponder gene expression phenotype is influenced by clinical factors and uncover the cellular basis of the phenotype through ISG15 protein expression.

METHODS

Seventy-eight CHC patients undergoing treatment were classified by clinical (gender, viral genotype, viral load, treatment outcome) and histologic (inflammation, fibrosis) factors and subjected to gene expression profiling on their pretreatment liver biopsies. An analysis of variance model was used to study the influence of individual factors on gene expression. ISG15 immunohistochemistry was performed on a subset of 31 liver biopsy specimens.

RESULTS

One hundred twenty-three genes were differentially expressed in the 78 CHC livers when compared with 20 normal livers (P < .001; fold change, > or =1.5-fold). Of genes influenced by a single factor, genotype (1 vs 2/3) influenced more genes (17) than any other variable; when treatment outcome was included in the analysis, this became the predominant influence (24 genes), and the effect of genotype was diminished. Treatment response was linked to cell-specific activation patterns: ISG15 protein up-regulation was more pronounced in hepatocytes in treatment nonresponders but in Kuppfer cells in responders.

CONCLUSIONS

Genotype is a surrogate marker for the nonresponder phenotype. This phenotype manifests as differential gene expression and is driven by activation of different cell types: hepatocytes in treatment nonresponders and macrophages in treatment responders.

Preparation of polyclonal antibody against human MxA protein and its specificity to diversified myxovirus resistant protein A

OBJECTIVE

To study the human myxovirus resistant protein A (MxA), a specifically induced peptide by interferon I, and to use its level as a diagnostic criterion for viral infections.

METHODS

Anti-MxA antisera from immunized mice were prepared with the expressed MxA protein of pET32a-MxA in E. coli BL-21(DE3). To confirm the antiserum activity and specificity, the expression product of BL21, wild type MxA pEGFP-C1-wMxA and site-directed mutant MxA pEGFP-C1-mMxA(N589S) stably transfected 3T3 cells and induced A549 cells were detected by Western blot with the antisera using non-MxA transfected or non-IFN-beta induced cells, intact A549, NIH 3T3 cells transfected with pEGFP-C1 and pET32a (+)-transformed BL-21 as controls.

RESULTS

The antisera had specific positive immunoreactivity to the NIH3T3 cells transformed with pEGFP-C1-wMxA and pEGFP-C1-mMxA, INF-beta induced A549 cells and BL21 proteins expressed with pET32a (+)-MxA. The hybridization signals from IFN-beta induced A549 cells depended on the IFN-beta inducing concentrations. Meanwhile, immunohistochemical assay showed that NIH 3T3 cells with pEGFP-C1-wMxA and pEGFP-C1-mMxA had > 98% of positive cells at 1:50 dilution of the serum and A549 cells induced by 20 ng/mL IFN-beta for 48 h showed 95% positive cells. pEGFP-C1-transfected NIH 3T3 cells were all negative.

CONCLUSION

Anti-sera are highly specific to diversified MxAs. The antibody is detectable by Western blot, immunocytochemistry and immunofluorescence assay.

Genomic scale analysis of racial impact on response to IFN-alpha

Limited responsiveness to IFN-alpha in hepatitis C virus (HCV)-infected African-Americans compared to European Americans (AAs vs. EAs) hinders the management of HCV. Here, we studied healthy non-HCV-infected AA and EA subjects to test whether immune cell response to IFN-alpha is determined directly by race. We compared baseline and IFN-alpha-induced signal transducer and activator of transcription (STAT)-1, STAT-2, STAT-3, STAT-4, and STAT-5 protein and phosphorylation levels in purified T cells, global transcription, and a genomewide single-nucleotide polymorphism (SNP) profile of healthy AA and EA blood donors. In contrast to HCV-infected individuals, healthy AAs displayed no evidence of reduced STAT activation or IFN-alpha-stimulated gene expression compared to EAs. Although >200 genes reacted to IFN-alpha treatment, race had no impact on any of them. The only gene differentially expressed by the two races (NUDT3, P < 10(-7)) was not affected by IFN-alpha and bears no known relationship to IFN-alpha signaling or HCV pathogenesis. Genomewide analysis confirmed the self-proclaimed racial attribution of most donors, and numerous race-associated SNPs were identified within loci involved in IFN-alpha signaling, although they clearly did not affect responsiveness in the absence of HCV. We conclude that racial differences observed in HCV-infected patients in the responsiveness to IFN-alpha are unrelated to inherent racial differences in IFN-alpha signaling and more likely due to polymorphisms affecting the hosts' response to HCV, which in turn may lead to a distinct disease pathophysiology responsible for altered IFN signaling and treatment response.

Expression of interferon-alpha and Mx protein in the livers of pigs experimentally infected with swine hepatitis E virus

Expression of interferon-alpha (IFN-alpha) and Mx protein in the livers of pigs experimentally infected with swine hepatitis E virus (HEV) was examined immunohistochemically. Five infected and five non-infected pigs were killed at 3, 7, 14, 21, 29 and 50 days post-inoculation (dpi). Tissues were collected from each pig at necropsy. Multifocal lymphoplasmacytic hepatitis (P=0.042) and focal hepatocellular necrosis (P=0.037) were significantly more frequent in the swine HEV-infected pigs than in the non-infected control pigs. Immunohistochemical analysis detected expression of IFN-alpha and Mx protein by macrophages/Kupffer cells, lymphocytes and hepatocytes in the livers of infected pigs.

Expression of the interferon-inducible proteins MxA and IFI16 in liver allografts

AIMS

To test the hypothesis that the activation of the interferon (IFN) system pathways might link hepatitis C virus (HCV) recurrence in the liver allograft with acute cellular rejection.

METHODS AND RESULTS

In this retrospective study, allograft biopsy specimens from 28 adult patients (14 HCV+ and 14 HCV-) who had undergone their first liver transplantation were analysed. Eleven biopsy specimens showed acute cellular rejection (Banff rejection activity index score > or =3). Specimens were immunostained for two IFN-inducible proteins, MxA and IFI16, and for CD45. The predominant MxA reactivity pattern was hepatocytic, whereas IFI16 was expressed in both the hepatocellular and inflammatory compartments. Moderate to strong MxA expression in hepatocytes was associated positively with rejection score (P < 0.01), donor's age < or =45 years (P < 0.05) and aspartate aminotransferase levels >40 U/l on the day of biopsy (P < 0.05), and inversely with infiltration of portal triads by IFI16+/CD45+ cells (P < 0.005) and time to progression beyond Ishak stage 2 of recurrent hepatitis C (P < 0.01). On multivariate analysis, MxA expression in hepatocytes was independently associated with allograft rejection and donor's age.

CONCLUSIONS

Acute allograft rejection and recurrence of HCV infection in the liver allograft appear to intersect in the IFN system pathways.

Hepatocellular MxA protein expression supports the differentiation of recurrent hepatitis C disease from acute cellular rejection after liver transplantation

Differentiation of recurrent hepatitis C virus (HCV) disease from acute cellular rejection (ACR) following liver transplantation can be difficult. Previously, we have found that MxA protein, a specific and sensitive marker for type 1 interferon production, is strongly expressed in chronic HCV disease. Here, we investigate MxA expression as a marker for recurrent HCV disease in the livers of 14 adult HCV patients who underwent liver transplantation. Serial liver biopsies available for 12 of these patients were stained for MxA protein and scored using a semi-quantitative approach. Hepatocellular MxA protein levels were significantly up-regulated (p = 0.025) in recurrent HCV disease in comparison to ACR. In biopsies that showed histological changes consistent with recurrent HCV disease, strong hepatocellular MxA staining was present in 14/18 (78%). In the liver biopsies with histological evidence of ACR, strong MxA hepatocellular staining was present in only three of 10 (30%). Thus, assessment of hepatocellular MxA protein expression can contribute to the differential diagnosis of ACR and recurrent HCV disease following liver transplantation. In conclusion, analysis of intrahepatic MxA levels has the potential to reduce the inappropriate use with high-dose pulsing of steroids post-operatively.

Ultra-structural localisation of hepatocellular PKR protein using immuno-gold labelling in chronic hepatitis C virus disease

The greater resistance of HCV genotype 1 infection to IFN therapy has been partially attributed to functional inhibition of the type 1 interferon induced anti-viral protein PKR in vitro. Whether PKR has antiviral activity against HCV in vivo is unknown. Whilst the ultra-structural localisation of PKR is known in vitro, it is not defined in chronic hepatitis C disease. Using a novel immuno-gold technique we characterised the expression of intrahepatic PKR protein at the ultra-structural level in four patients with chronic HCV disease compared to normal human PBMCs, HepG2 cells and a normal human liver biopsy. All four HCV patients labelled for PKR protein, localising to the nucleus, nucleolus and cytoplasm. Nuclear labelling was confined mainly to the nucleolus and euchromatin. Cytoplasmic labelling was evident within smooth vesicles. Strong immunogold labelling was also evident within the cisternae of the rough endoplasmic reticulum. A similar pattern of ultra-structural nuclear and cytoplasmic PKR protein labelling was seen in PBMCs from healthy donors, HepG2 cells and a normal liver biopsy. The mean nuclear and cytoplasmic count for PKR protein in the HCV group was 21 +/- 4 and 18 +/- 3 gold particles/microm(2), respectively. This represented an increase, though not statistically significant, in nuclear and cytoplasmic labelling for PKR protein in HCV biopsies relative to normal liver tissue.

Hepatic SOCS3 expression is strongly associated with non-response to therapy and race in HCV and HCV/HIV infection

BACKGROUND/AIMS

The response rates of HCV infection to interferon therapy vary depending on viral and host factors. We hypothesized that key regulators of the IFN signaling pathway are predictive of treatment outcome.

METHODS

We measured the expression of signal transducer and activator of transcription 1 (STAT1) and suppressor of cytokine signaling 3 (SOCS3) in pretreatment liver biopsies. Staining quantitation was compared to treatment outcomes.

RESULTS

Forty-nine patients with HCV and 25 patients with HCV/HIV infection treated with peginterferon/ribavirin were analyzed. Pretreatment hepatic SOCS3 expression was higher in non-responders than responders. Genotype 1 responders had similar levels of SOCS3 as genotype 2/3 responders. African Americans (AA) had higher hepatic SOCS3 than non-AA. Pretreatment hepatic SOCS3 was the most powerful independent predictor of sustained virologic response (SVR), even more so than genotype by logistic regression analysis. Failure to achieve SVR and AA race were independently associated with high hepatic SOCS3 levels. The hepatic expression of STAT-1 did not differ between responders and non-responders.

CONCLUSIONS

Our data indicate that hepatic SOCS3 is a stronger baseline predictor of antiviral response than viral genotype. Poor response to antiviral therapy in AA may be associated with higher hepatic SOCS3 expression.

Interferon-Induced Effector Proteins and Hepatitis C Virus Replication

Hepatitis C virus (HCV) is a small, enveloped RNA virus that is often capable of establishing a persistent infection, which may lead to chronic liver disease, cirrhosis, hepatocellular carcinoma, and eventually death. For more than 20 years, hepatitis C patients have been treated with interferon-alpha (IFN-α). Current treatment usually consists of polyethylene glycol-conjugated IFN-α that is combined with ribavirin, but even the most advanced IFN-based therapies are still ineffective in eliminating the virus from a large proportion of individuals. Therefore, a better understanding of the IFN-induced innate immune response is urgently needed. By using selectable self-replicating RNAs (replicons) and, more recently, recombinant full-length genomes, many groups have tried to elucidate the mechanism(s) by which IFNs inhibit HCV replication. This chapter attempts to summarize the current state of knowledge in this interesting field of HCV research.

Hepatitis C virus expression and interferon antiviral action is dependent on PKR expression

Interferon (IFN)-inducible double-stranded RNA-activated protein kinase (PKR) is thought to play a key antiviral role against hepatitis C virus (HCV). However, demonstrating the importance of PKR expression on HCV protein synthesis in the presence or absence of IFN has proven difficult in vivo. In the present experiment, full-length HCV constructs were transiently transfected into two cell lines stably expressing T7 RNA polymerase. HCV expression was monitored under conditions of upregulated or downregulated PKR expression. In addition, IFN was monitored during downregulation of PKR. HCV expression effectively increased PKR expression, as well as that of its regulated proteins. PKR was obviously knocked down by PKR-specific siRNA, which resulted in significantly increased HCV core protein levels. Conversely, over-expression of PKR significantly suppressed HCV core levels in both cell lines. Furthermore, IFN induced high levels of PKR, whereas downregulation of PKR reversed IFN's antiviral effects and increased HCV core levels. Based on these results, it appears that HCV protein expression is directly dependent on PKR expression. PKR is antiviral toward HCV and responsible for IFN's effect against HCV.

Expression of biomarkers of interferon type I in patients suffering from chronic diseases

Interferons (IFNs) are used widely in the treatment of viral infections, tumours and neurological disorders. The aim of this study was to evaluate the endogenous expressions of various IFN-induced compounds [specifically: neopterin (NPT), beta2microglobulin (beta2mg) and 2-5 oligoadenylate synthetase (2-5 OAS)] in patients with various chronic diseases requiring treatment with IFN type I. The results showed that patients with such chronic diseases as hepatitis C virus-associated type II mixed cryoglobulinaemia (MC), chronic hepatitis C (CHC) and relapsing-remitting multiple sclerosis (RRMS) are characterized by different activations of the IFN system. Furthermore, the interindividual variability in baseline levels of IFN-induced biomarkers was higher in patients with chronic diseases than in healthy individuals. When levels of the above biomarkers were measured 24 h after the first injection of IFN in patients with CHC or RRMS, significant increases in expression levels of IFN-induced compounds were recorded but, again, there is a broad range of variability in the degree of increase. Further, a significant inverse correlation between baseline levels of NPT, beta2mg and 2-5 OAS activity and their relative increases after IFN administration was found in patients with CHC or RRMS. Together, the results are consistent with the observation that there is considerable interindividual heterogeneity in the clinical response to IFNs, which suggests that host factors other than disease markers must be taken into account in order to manage and optimize the IFN therapy.

Hepatitis C virus infection--pathobiology and implications for new therapeutic options

Despite progress in therapeutic approaches for the elimination of hepatitis C, chronic hepatitis C virus infection remains an important cause of liver disease. Therapeutic intervention with the currently available interferon-based treatment regimens is quite successful, but treatment is difficult to tolerate and is contraindicated in many patients. A better understanding of the HCV biology, immunopathology, and liver disease will help to design better therapeutic strategies. The American Association for the Study of Liver Diseases sponsored a single-topic conference on hepatitis C virus infection on March 4 and 5, 2005, to enhance our current knowledge in the areas of basic and clinical research related to antiviral and immunomodulatory therapies in hepatitis C disease. The faculty consisted of 23 invited experts in the field of viral hepatitis. The program was divided into four sections including: (a) replicative mechanisms and models; (b) viral-host interactions; and (c) antiviral drug development and new strategies; and (d) back to the bedside-current issues. This report summarizes each of the presentations sections.

Expression of toll-like receptors and type 1 interferon specific protein MxA in biliary atresia

Viral infection and type I interferon have been implicated in the pathogenesis of biliary atresia (BA), but the expression of toll-like receptors (TLRs) that recognize viruses, as well as of type 1 interferon specific signaling molecules are still unknown in BA. Fresh liver tissues were obtained from patients in early and late stage of BA and from patients with choledochal cyst (CC), as well as from normal controls receiving liver resection for benign lesion other than cholestasis or fibrosis. Archived liver tissues from patients with neonatal hepatitis (NH) were obtained for immunohistochemical studies. TLR2, 3, 4, 7 and 9 that recognized Gram-positive bacteria, double-stranded RNA virus, lipopolysaccharide, single-stranded RNA virus and DNA virus, respectively, were studied. Real-time quantitative reverse transcription polymerase chain reaction (QRT-PCR) was used to quantitate TLR, type I interferon specific molecule MxA, interleukin-6 (IL-6) and IL-8 mRNA expression and immunohistochemistry for TLR 7 and MxA protein staining. These results show that there were significantly higher TLR7 and lower TLR3 and TLR9 mRNA expression in early stage of BA than in CC. MxA mRNA expression was also significantly higher in early stage of BA and in CC than in late stage of BA. Immunoreactive TLR7 and MxA staining was higher in early stage of BA than in late stage of BA, NH and CC, which was associated with significantly higher IL-8 mRNA expression in BA than in CC. The results implicate involvement of TLRs, particularly TLR7, and type 1 specific interferon signaling in the pathogenesis of BA, especially in early stage, which is associated with upregulation of inflammatory cytokines IL-8.

Drug abuse, innate immunity and hepatitis C virus

Since its discovery in 1989, hepatitis C virus (HCV) has become a major public health problem. HCV chronically infects an estimated 170 million people worldwide. The seroprevalence of anti-HCV antibody in the United States has been estimated at 1.8%, which corresponds to approximately 4 million people. HCV is the most common chronic blood borne infection in the United States, and the leading cause of liver transplantation in developed countries. Injection drug use is the dominant mode of HCV transmission and accounts for up to 90% of current infections. Opiates and other drug abuse, such as alcohol, have been implicated as cofactors in the pathogenesis of HCV disease. Injection drug use has been the most common risk factor identified in alcoholics with HCV infection. Both opiates and alcohol contribute significantly to morbidity and mortality from HCV disease. These drugs most likely act synergistically to promote the development and progression of HCV disease. However, there is limited information available concerning the interaction of the drug abuse with the host cell innate immunity against HCV infection, which is a major barrier to fundamental understanding of the immunopathogenesis of HCV disease. Therefore, defining the role of the drug abuse in the development of chronic HCV infection is of crucial importance and should provide practical guidance toward the reduction of risk factors that interfere with therapeutic approaches for HCV infection and disease. This review paper focuses on the interplay between drug abuse (opiates and alcohol), innate immunity and HCV in the context of the development of HCV disease.

Hepatitis C virus inhibits intracellular interferon alpha expression in human hepatic cell lines

The chronicity of hepatitis C virus (HCV) infection raises the question of how HCV is able to persist in hepatic cells. We show that human primary hepatocytes and human hepatic cell lines (Huh7 and HepG2) spontaneously produce interferon (IFN)-alpha that is inhibited in the HCV replicon cells (Huh.8 and FCA-1). Silencing IFN-alpha gene expression by IFN-alpha small interfering RNA (siRNA) in the HCV replicon cells resulted in increased HCV replicon expression. The activation of IFN-alpha expression by interferon regulatory factor (IRF-7) led to the inhibition of HCV replicon expression, whereas the anti-IFN-alpha receptor antibody could partially block IRF-7-mediated HCV replicon inhibition. In addition, the blockade of IFN-alpha receptor by anti-IFN-alpha receptor antibody on the replicon cells increased HCV replicon expression. Among the HCV nonstructural (NS) proteins tested, NS5A is the most potent inhibitor of IFN-alpha expression by the hepatic cells. Investigation of the mechanism of HCV action on IFN-alpha showed that IRF-7-induced IFN-alpha promoter activation was inhibited in the HCV replicon cells. Furthermore, IRF-7 expression was restricted in the HCV replicon cells. In conclusion, we provide direct evidence that HCV undermines the intracellular innate immunity of the target cells, which may account for HCV persistence in hepatic cells.

Salient molecular features of hepatitis C virus revealed

Hepatitis C virus (HCV) is a positive strand RNA virus with a narrow host and tissue tropism. It ranks among the most significant of human pathogens, causing inflammation, scarring and cancer of the liver. Recent investigations have shed light on some of the salient molecular features of this virus. These include a requirement for CD81 (a tetraspanin transmembrane protein for viral entry), a novel mechanism for the initiation of RNA synthesis, phosphorylation of a viral protein in the regulation of RNA amplification and virus assembly and, finally, a viral protease suppressing activation of the innate immune response in infected cells.

Interferon-stimulated gene expression in black and white hepatitis C patients during peginterferon alfa-2a combination therapy

BACKGROUND & AIMS

Black American patients are less likely to eradicate hepatitis C virus (HCV) infections during treatment with peginterferon (PEG-IFN) and ribavirin. We hypothesized that racial differences in IFN-stimulated antiviral gene induction during treatment might be responsible.

METHODS

We examined myxovirus resistance-A (MxA), RNA-dependent protein kinase (PKR), 2'-5' oligoadenylate synthetase (2,5-OAS), and adenosine deaminase-1 (ADAR1) gene expression in the peripheral blood mononuclear cells (PBMCs) of 31 black and 11 white HCV genotype 1 patients at baseline and at weeks 4-12 during PEG-IFN alfa-2a combination treatment. The primary study end point was the early virologic response (EVR)-either an undetectable serum HCV-RNA level or a > or =2-log decrease in serum HCV-RNA level at week 12 compared with week 0.

RESULTS

The EVR rate was 67.7% in blacks and 63.6% in whites. Both blacks and whites experienced a significant (200%-500%) increase in 2,5-OAS, MxA, PKR, and ADAR1 expression at treatment weeks 4-12 compared with baseline (P < .01). However, the relationship between IFN-stimulated gene expression and the EVR differed by race. White responders exhibited higher 2,5-OAS and MxA levels at week 4 than white nonresponders (P < .05). IFN-stimulated gene levels did not correlate with EVR in blacks. Black responders had much lower MxA and PKR levels at week 4 than black nonresponders (P < .05). However, black responders maintained increased 2,5-OAS, MxA, and PKR levels from weeks 4-12, whereas the levels decreased to baseline at weeks 8-12 in black nonresponders.

CONCLUSIONS

The mechanisms of resistance to PEG-IFN combination therapy may be different in black and white HCV genotype 1 patients.

Hepatic gene expression discriminates responders and nonresponders in treatment of chronic hepatitis C viral infection

BACKGROUND & AIMS

Pegylated interferon (IFN)-alpha plus ribavirin is the most effective treatment of chronic hepatitis C but has unpleasant side effects and high costs. A large proportion of patients do not respond to therapy for reasons that are unclear. We used gene expression profiling to investigate the molecular basis for treatment failure.

METHODS

Expression profiling was performed on percutaneous needle liver biopsy specimens taken before therapy. Gene expression levels were compared among 15 nonresponder, 16 responder, and 20 normal liver biopsy specimens. Differential gene expression was confirmed using real-time polymerase chain reaction.

RESULTS

We identified 18 genes whose expression differed significantly between all responders and all nonresponders (P < .005). Many of these 18 genes are IFN sensitive and 2 (ISG15/USP18) are linked in a novel IFN-regulatory pathway, suggesting a possible rationale for treatment resistance. Using a number of independent classifier analyses, an 8-gene subset accurately predicted treatment response for 30 of 31 patients. The classifier analyses were applicable to patients with genotype 1 infection and were not correlated with viral load, disease activity, or fibrosis.

CONCLUSIONS

Hepatic gene expression profiling identified consistent differences in patients who subsequently fail treatment with pegylated IFN-alpha plus ribavirin: up-regulation of a specific set of IFN-responsive genes predicts nonresponse to exogenous therapy. These data may be of use in predicting clinical responses to treatment.

MxA and PKR expression in chronic hepatitis C

The effectiveness of therapy for chronic hepatitis C (CHC) patients has greatly improved in the last few years, and the gold standard is currently held to be pegylated interferon (IFN) in combination with ribavirin. Overall, however, the percentage of patients achieving a sustained virologic response (SVR) is only around 50%,and it is not possible to predict those patients who will benefit from therapy. The molecular mechanisms underlying lack of therapeutic response remain unknown. In this study, we investigated the tissue expression of MxA and RNA-dependent protein kinase (PKR), two antiviral proteins modulated by IFN, in biopsy samples from hepatitis C patients before the beginning of therapy. Our results show that expression of MxA, but not of PKR, is significantly lower in responders compared with nonresponders. No differences were observed regarding the hepatitis C virus (HCV) genotype and the viral load. These results suggest that expression of the MxA protein could play a role among the mechanisms underlying responsiveness to therapy.

Novel insights into hepatitis C virus replication and persistence

Hepatitis C virus (HCV) is a small enveloped RNA virus that belongs to the family Flaviviridae. A hallmark of HCV is its high propensity to establish a persistent infection that in many cases leads to chronic liver disease. Molecular studies of the virus became possible with the first successful cloning of its genome in 1989. Since then, the genomic organization has been delineated, and viral proteins have been studied in some detail. In 1999, an efficient cell culture system became available that recapitulates the intracellular part of the HCV life cycle, thereby allowing detailed molecular studies of various aspects of viral RNA replication and persistence. This chapter attempts to summarize the current state of knowledge in these most actively worked on fields of HCV research.

Reduction of double-stranded RNA-activated protein kinase in hepatocellular carcinoma associated with hepatitis B virus

Chronic hepatitis B virus (HBV) infection is a major cause of hepatocellular carcinoma (HCC) in Asia. Double-stranded RNA (dsRNA)-activated protein kinase (PKR) is an interferon-induced, serine/threonine protein kinase. Recent studies have suggested that PKR is involved in the pathogenesis of HCC with hepatitis virus C infection by inhibiting viral and cellular proteins related to cell growth and proliferation. In the present study, PKR was examined in both tumor and non-tumor tissues from HCC livers infected with HBV. The expression of PKR was determined by TaqMan real-time PCR and immunohistochemical methods. The level of PKR was also analyzed in relation to pathological changes observed in HCC. The result showed that PKR was reduced in tumor tissues of HCC from HBV carriers with low serum viral load (<0.7 x 10(6) copies/ml) compared to those with higher serum viral load. However, the overall PKR level was much lower in tumor tissues than that in non-tumor tissues, irrespective of HBV carrier status or serum viral load. PKR level tended to be lower in HCC samples with alpha-fetoprotein (AFP) more than 500 ng/ml (mean: 4024.2 ng/ml) than those with AFP less than 500 ng/ml (mean: 50.6 ng/ml). There was no significant difference in the expression of PKR between tumor tissues with well differentiation and those with poor or moderate differentiation. In conclusion, the level of PKR was reduced in HCC tumor tissues, suggesting a possible role of PKR in promoting the growth of tumor. HBV may participate in altering the level of PKR, but factors other than HBV should play a more determining role in the regulation of PKR in HCC. The association between PKR and AFP levels may offer an alternative tumor marker for HCC.

Pkr Gene Expression and Response to Pegylated Interferon plus Ribavirin Therapy in Chronic Hepatitis C

Pegylated interferon (PEG-IFN) alpha combined with ribavirin is the current standard treatment for hepatitis C, but around 50% of patients do not respond for reasons that are not fully understood. To explore the regulation of IFN-inducible protein kinase (PKR), we have measured PKR mRNA levels in peripheral blood mononuclear cells (PBMCs) and in liver biopsies from patients with chronic hepatitis C. PBMCs were also analysed after in vitro incubation with IFN and during antiviral therapy. Non-responders to PEG-IFN plus ribavirin had pre-treatment PKR mRNA levels in PBMCs (0.1 ±0.0074) and in liver (0.102 ±0.051) that were significantly higher than those of responders (PBMCs: 0.023 ±0.014, P=0.0005; liver: 0.034 ±0.020; P=0.0002). On the other hand, PKR mRNA levels in PBMCs were similar in non-responders and in responders after in vitro exposure to IFN (0.434 ±0.301 vs 0.403 ±0.222; P=NS) and during therapy (0.31 ±0.10 vs 0.30 ±0.12; P=NS). These results indicate that in hepatitis C, non–responsiveness to IFN-alpha is associated with pre-treatment up-regulation of the PKR gene, evidence that the infecting hepatitis C virus is able to stimulate endogenous IFN production, being resistant to its antiviral effect. On the other hand, the PKR gene response to exogenous IFN was similar in responders and non-responders, at least in PBMCs, suggesting that variations in its activation are not major determinants of the outcome of antiviral treatment.